Process for the preparation of a cumene feed for cumene oxidation

ABSTRACT

A process for the preparation of a cumene feed for cumene oxidation from a fresh cumene stream and a recycle cumene stream containing trace quantities of at least one organic acid compound by means of introducing the fresh cumene stream and the recycle cumene stream containing trace quantities of an organic acid compound into a lower zone of a generally vertical elongated countercurrent contacting zone having a caustic/hydrocarbon contacting section in a lower portion of the countercurrent contacting zone and a water/hydrocarbon contacting section in an upper portion of the countercurrent contacting zone; introducing a water stream to provide water to the water/hydrocarbon contacting section; including an aqueous caustic scrubbing solution to provide caustic solution to the caustic/hydrocarbon contacting section; removing spent aqueous caustic solution from the countercurrent contacting zone; and removing and recovering a cumene feed from the countercurrent contacting zone.

BACKGROUND OF THE INVENTION

The field of art to which this invention pertains is the preparation ofa cumene feed for a cumene oxidation process. More specifically, theinvention relates to a process for the preparation of a cumene feed forcumene oxidation from a fresh cumene stream and a recycle cumene streamcontaining trace quantities of at least one organic acid compound.

In general, phenols are prepared by the oxidation of a secondaryalkylbenzene and the subsequent acid cleavage of the resulting alpha,alpha-dialkybenzyl hydroperoxide to form a reaction mixture comprising aphenol, a ketone and unreacted secondary alkylbenzene. The acid cleavageis generally effected in the presence of an aqueous acid catalyst,usually sulfuric acid or sulfur dioxide in aqueous solution, or in thepresence of an aqueous hydrochloric or perchloric acid solution. Thepresent invention is particularly directed to a process wherein phenolis prepared by the air oxidation of cumene and the subsequent sulfuricacid cleavage of the resulting cumene hydroperoxide to form a reactionmixture comprising phenol, acetone and unreacted cumene. In addition tothe principal products, there are formed varying amounts of by-productssuch as mesityl oxide, alpha-methylstryrene, p-cumylphenol,phenyldimethylcarbinol, acetophenone, and higher molecular weightphenols.

In the process of recovering phenol from the acid cleavage reactionmixture, the acidic reaction mixture is initially neutralized, eitherdirectly by the addition of caustic, or indirectly by contact with anion exchange resin. In any case, the neutralized reaction mixture is fedto a distillation column, commonly referred to as a crude acetonecolumn, at conditions to effect a crude separation of those materialsboiling below phenol whereby an overhead fraction is recoveredcomprising substantially all of the acetone and lower boilingby-products, as well as a substantial portion of the water and unreactedcumene. Acetone is subsequently recovered, as is cumene, by the furtherdistillation of the crude acetone column overhead. The resultingrecovered cumene is recycled to the oxidation process.

The bottoms fraction recovered from the crude acetone column, comprisingphenol and alpha-methylstyrene as well as the balance of the water andunreacted cumene, is typically treated for the separation of heavy endsand thereafter fed to a distillation column, commonly referred to as acumene or alpha-methylstyrene column. The latter column is operated atconditions to separate an overhead fraction comprising water, cumene andalpha-methylstyrene from the higher boiling phenol product. The phenol,recovered as the bottoms fraction, further contains certain impurities,e.g., mesityl oxide and hydroxy acetone, and said impurities are treatedand separated from this bottoms fraction to yield a substantially purephenol product.

The overhead fraction from the cumene column will invariably comprise asignificant amount of phenol as well as cumene and alpha-methylstyrene.It has been the practice to caustic-extract this overhead fraction andthe cumene and the alpha-methylstyrene recovered as a water-immiscibleorganic phase is separated and recycled to oxidation as cumene. Thephenol is recovered as sodium phenate in the aqueous phase, a practicewhich has necessitated a separate phenol recovery facility wherein theaqueous sodium phenate solution is acid treated and the resulting phenolbeing recycled and combined with the acid cleavage product for recoveryas hereinabove described, and the acidifying agent being subsequentlyextracted with a solvent or stripped with steam for economical recoverywith phenol, followed by necessary treatment for safe disposal.

The total charge to the oxidation section of a phenol process unitconsists of fresh cumene and recycle cumene from other various sectionsof the unit, i.e., from the spent air treating section, from theconcentration section and from the fractionation section. The recyclecumene from the fractionation section normally would have undergone acaustic wash with a 5-30 weight percent caustic solution for the purposeof extracting the phenol and would be basic in nature due to theentrained caustic solution. The cumene recovered from the spent air andfrom the concentration sections, however, contains small quantities oforganic acid compounds which are undesirable in the phenol process unit.

It is therefore necessary to caustic wash the recycle streams and isalso desirable to wash the fresh cumene charged to the oxidizer with atleast a dilute caustic solution. It is also important that a water washbe performed after the caustic wash in order to remove the entrainedcaustic since a breakthrough of the caustic to the decomposer wouldneutralize the small quantity of acid catalyst in the decomposer.

The prior art teaches that the caustic wash and the water wash may beperformed in a complex manner and those skilled in the prior art havesought a more efficient process to prepare a cumene feed for cumeneoxidation. We have discovered a process for achieving this result whichis less complex, more economical and more space efficient.

Previously, it was also advantageous to caustic wash and water wash theoxidizer effluent to remove traces of organic acids, i.e., formic acid,that are formed in the oxidation reaction in order to prevent corrosionin the downstream sections, especially in the fractionation section. Inthe prior art processes, the waste aqueous phase is normally sent to acumene extraction column where the cumene hydroperoxide is extractedfrom the aqueous phase by using a slipstream of the fresh cumene chargewhich is then sent to the oxidizer.

In accordance with the present invention, the total feed caustic washand/or the cumene extraction column is replaced by a single contactertower as described hereinafter. This single contacter tower issuccessfully used to achieve a process for the preparation of a cumenefeed for cumene oxidation which is less complex, more economical andspace efficient.

BRIEF SUMMARY OF THE INVENTION

The invention provides a process for the preparation of a cumene feedfor cumene oxidation from a fresh cumene stream and a recycle cumenestream containing trace quantities of at least one organic acid compoundby means of introducing the fresh cumene stream and the recycle cumenestream containing trace quantities of an organic acid compound into alower zone of a generally vertical elongated countercurrent contactingzone having a caustic/hydrocarbon contacting section in a lower portionof the countercurrent contacting zone and a water/hydrocarbon contactingsection in an upper portion of the countercurrent contacting zone;introducing a water stream to provide water to the water/hydrocarboncontacting section; introducing an aqueous caustic scrubbing solution toprovide caustic solution to the caustic/hydrocarbon contacting section;removing spent aqueous caustic solution from the countercurrentcontacting zone; and removing and recovering a cumene feed from thecountercurrent contacting zone. Important elements of the improvedprocess are less complex equipment requirements, more economicaloperation and more efficient use of plot space. In accordance with thepresent invention, the total feed caustic wash and the cumene extractioncolumn found in the prior art processes may be advantageously replacedby a single contacting tower as described herein.

One embodiment of the present invention may be characterized as aprocess for the preparation of a cumene feed for cumene oxidation from afresh cumene stream and a recycle cumene stream containing tracequantities of at least one organic acid compound which processcomprises: (a) introducing the fresh cumene stream and the recyclecumene stream containing trace quantities of at least one organic acidcompound into an intermediate, lower locus of a generally vertical,elongated, countercurrent contacting zone having a caustic/hydrocarboncontacting section in a lower portion of the countercurrent contactingzone and a water/hydrocarbon contacting section in an upper portion ofthe countercurrent contacting zone; (b) introducing a water stream intoan intermediate, upper locus of the countercurrent contacting zone atthe top of the water/hydrocarbon contacting section to provide water tothe water/hydrocarbon contacting section; (c) introducing an aqueouscaustic scrubbing solution into an intermediate locus of thecountercurrent contacting zone at the top of the caustic/hydrocarboncontacting section to provide caustic solution to thecaustic/hydrocarbon contacting section; (d) removing spent aqueouscaustic solution from the countercurrent contacting zone at a bottomlocus of the countercurrent contacting zone at the bottom of thecaustic/hydrocarbon contacting section; and (e) removing a cumene feedfrom the countercurrent contacting zone at an upper locus of thecountercurrent contacting zone at the top of the water/hydrocarboncontacting section.

Another aspect of the invention is the staging of the hydrocarbon streaminjection points, i.e., the fresh cumene and the recycle cumene from thefractionation section is preferably introduced at a location below theintroduction location of the other combined recycle streams, includingrecycle from the concentration section and recycle cumene from the spentair treatment decanter.

Cumene hydroperoxide (CHP) is somewhat soluble in caustic and thesolubility increases with caustic concentration. The other combinedrecycle streams, including recycle from the concentration section andrecycle cumene from the spent air treatment decanter, contain CHP, aportion of which is carried by the caustic wash on its downward paththrough the countercurrent contacting zone. By contacting the spentcaustic with fresh cumene and the recycle stream from fractionation,both of which contain negligible amounts of CHP, the CHP in the flowingcaustic waste stream is re-extracted and returned to the hydrocarbonphase which minimizes the loss of CHP and increases product yields.

Other embodiments of the present invention encompass further detailssuch as preferred cumene feed streams, aqueous caustic scrubbingsolutions and operating conditions, all of which are hereinafterdisclosed in the following discussion of each of these facets of theinvention.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a simplified process flow diagram of a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The overall process to which this invention pertains concerns theoxidation of a secondary alkylbenzene, for example, isopropylbenzene(cumene) isobutylbenzene, isoamylbenzene, 1-methyl-4-isopropylbenzene,p-diisopropylbenzene, p-diisobutylbenzene,1-isopropyl-4-isobutylbenzene, cyclohexyl benzene, and the like, to formthe corresponding hydroperoxide, i.e., isopropylbenzene hydroperoxide,isobutylbenzene hydroperoxide, isoamylbenzene hydroperoxide,1-methyl-4-isopropylbenzene hydroperoxide, p-diisopropylbenzenehydroperoxide, p-diisobutylbenzene hydroperoxide,1-isobutyl-4-isopropylbenzene dihydroperoxide, cyclohexylbenzenehydroperoxide, and the like. The present invention is particularlydirected to a process for the preparation of a cumene feed for cumeneoxidation from a fresh cumene stream and a recycle cumene streamcontaining trace quantities of at least one organic acid compound. Theorganic acid compound is expected from the group consisting of formicacid, acetic acid, benzoic acid, propionic acid and butyric acid.

The aforesaid oxidation reaction is effected at conditions well known inthe art. The hydroperoxide oxidation product can be prepared by directliquid phase oxidation of the selected alkylbenzene with oxygen, or anoxygen-containing gas such as air, usually at an elevated temperature.The oxidation reaction proceeds slowly through an initial inductionperiod, accelerating to a more favorable rate with the formation of thehydroperoxide which exerts a catalytic effect on the oxidation reaction.This initial induction period is eliminated, or substantially reduced,by initially including a hydroperoxide in the reaction mixture, usuallythe hydroperoxide product of the reaction. However, other materials aredisclosed in the art which exhibit a similar catalytic effect.Temperatures effecting the oxidation reaction range from about roomtemperature to about the boiling point of the hydrocarbon subjected tooxidation, which, in the case of cumene, is about 305° F. In general, itis preferred to utilize an elevated temperature in the range of fromabout 120° to about 265° F. The optimum temperature will depend on theparticular alkylbenzene to be oxidized and on the reaction conditionsotherwise employed. The oxidation can be effected at pressures rangingfrom about atmospheric to about 500 psig, although a pressure notexceeding about 90 psig is generally preferred. It is desirable to limitthe contact time of the reactants at oxidation conditions to effectsubstantially less than complete conversion of the alkylbenzene to thecorresponding hydroperoxide. For example, in the oxidation of cumene, itis desirable to limit the contact time of the cumene and the oxidizingagent so that the concentration of the resulting cumene hydroperoxidedoes not exceed about 40 wt. %.

The vertical, countercurrent contacting zone of the present inventionhas a caustic/hydrocarbon contacting section in a lower portion of thecountercurrent contacting zone and a water/hydrocarbon contactingsection in an upper portion of the countercurrent contacting zone. Thecaustic/hydrocarbon section is where a downwardly flowing causticsolution is countercurrently contacted with an upwardly flowinghydrocarbon stream to remove trace quantities of organic acid from thehydrocarbon stream. The water/hydrocarbon contacting section is where adownwardly flowing fresh water stream is countercurrently contacted withan upwardly flowing hydrocarbon stream to remove trace quantities ofcaustic solution from the hydrocarbon stream. The fresh cumene andrecycle cumene are introduced at or near the bottom of thecountercurrent contacting zone and a cumene feed is removed from the topof the countercurrent contacting zone. A spent caustic stream is removedfrom the bottom of the countercurrent contacting zone and anothercaustic stream is circulated from the bottom of the countercurrentcontacting zone and introduced at the top of the water/hydrocarboncontacting section together with fresh caustic. Fresh water isintroduced at or near the top of the countercurrent contacting zonewhich is also the top of the water/hydrocarbon contacting stream.

In accordance with the present invention, the vertical, countercurrentcontacting zone is preferably contained in a vessel which has packing,trays or other convenient means to provide countercurrent liquid-liquidextraction. The contacting zone is preferably operated at a pressurefrom about atmospheric (0 kPa gauge) to about 50 psig (345 kPa gauge)and a temperature from about 41° F. (5° C.) to about 140° F. (60° C.).Any convenient operating temperature and pressure may be used in thepractice of the present invention.

In the water/hydrocarbon contacting zone the volumetric ratio of waterto hydrocarbon may range from about 1:100 to about 20:100, and in thecaustic/hydrocarbon contacting zone the volumetric ratio of aqueouscaustic solution to hydrocarbon may range from about 1:100 to about20:100.

The aqueous caustic solution which is introduced into thecaustic/hydrocarbon contacting zone preferably contains from about 0.1to about 5 weight percent caustic and the preferred caustic solution isan aqueous sodium hydroxide solution. Make-up caustic solutions may haveconcentrations from about 5 to about 50 weight percent caustic.

The further description of the process of this invention is presentedwith reference to the attached drawing. The drawing is a simplified flowdiagram of a preferred embodiment of this invention and is not intendedas an undue limitation on the generally broad scope of the invention asset out in the appended claims. Certain hardware such as valves, pumps,compressors, heat exchangers, instrumentation and controls, have beenomitted as not essential to a clear understanding of the invention. Theuse and application of this hardware is well within the skill of theart.

Referring now to the drawing, a fresh cumene stream and caustic washedrecycle stream from a fractionation section in an amount of 33,500pounds per hour and containing 10 weight ppm phenol is introduced viaconduit 1 into countercurrent contacting vessel 3. Combined recyclecumene streams consisting of cumene recovered from spent air and from aconcentration section in an amount of 91,406 pounds per hour andcontaining three weight percent cumene hydroperoxide, 50 weight ppmphenol and trace amounts of organic acid are introduced via conduit 2into countercurrent contacting vessel 3. These two combined streams ofcumene upon entering countercurrent contacting vessel 3 being to flow ina generally upward manner through water/hydrocarbon contacting zone 11and are contacted with a generally downwardly flowing aqueous causticstream in a countercurrent manner in order to extract organic acidcompounds and trace quantities of phenol which are introduced with thecumene streams. The upwardly flowing cumene then enters awater/hydrocarbon contacting zone 10 wherein the cumene iscountercurrently contacted with fresh water which is introduced intocountercurrent contacting vessel 3 via conduit 4. The fresh waterentering via conduit 4 is in an amount of 2,000 pounds per hour and isutilized to remove entrained caustic and to ensure a cumene feed streamwhich is essentially free of entrained aqueous caustic. A resultingcumene feed stream is removed from countercurrent contacting vessel 3via conduit 9 in an amount of 91,400 pounds per hour. This resultingcumene feed may then be coalesced to remove entrained water before it isintroduced into oxidizers to produce cumene hydroperoxide. An aqueouscaustic solution containing about 1 weight percent sodium hydroxide isremoved from the bottom of the countercurrent contacting vessel 3 viaconduit 6. At least a portion of this aqueous caustic stream isrecirculated via conduit 7 and pump 8 to provide an aqueous causticsolution for caustic/hydrocarbon contacting zone 11. The net causticsolution removed via conduit 6 from countercurrent contacting vessel 3is removed from the process and recovered for safe disposal. A freshaqueous caustic make-up stream in an amount of 82 pounds per hour andcontaining 27 weight percent sodium hydroxide is introduced into theprocess via conduit 5 and is then introduced into countercurrentcontacting vessel 3 via conduit 7.

The foregoing description and drawing clearly illustrate the advantagesencompassed by the process of the present invention and the benefits tobe afforded with the use thereof.

What is claimed:
 1. A process for the preparation of a cumene feed forcumene oxidation from a fresh cumene stream and a recycle cumene streamcontaining trace quantities of at least one organic acid compound whichprocess comprises:(a) introducing said fresh cumene stream and saidrecycle cumene stream containing trace quantities of at least oneorganic acid compound into an intermediate, lower locus of a generallyvertical, elongated, countercurrent contacting zone having acaustic/hydrocarbon contacting section in a lower portion of saidcountercurrent contacting zone and a water/hydrocarbon contactingsection in an upper portion of said countercurrent contacting zone; (b)introducing a water stream into an intermediate, upper locus of saidcountercurrent contacting zone at the top of said water/hydrocarboncontacting section to provide water to said water/hydrocarbon contactingsection; (c) introducing an aqueous caustic scrubbing solution into anintermediate locus of said countercurrent contacting zone at the top ofsaid caustic/hydrocarbon contacting section to provide caustic solutionto said caustic/hydrocarbon contacting section; (d) removing spentaqueous caustic solution from said countercurrent contacting zone at abottom locus of said countercurrent contacting zone at the bottom ofsaid caustic/hydrocarbon contacting section; and (e) removing a cumenefeed from said countercurrent contacting zone at an upper locus of saidcountercurrent contacting zone at the top of said water/hydrocarboncontacting section.
 2. The process of claim 1 wherein said organic acidcompound is selected from the group consisting of formic acid, aceticacid, benzoic acid, propionic acid and butyric acid.
 3. The process ofclaim 1 wherein said generally vertical, elongated countercurrentcontacting zone is operated at a pressure from about atmospheric (0 kPagauge) to about 50 psig (345 kPa gauge) and a temperature from about 41°F. (5° C.) to about 140° F. (60° C.).
 4. The process of claim 1 whereinsaid water/hydrocarbon contacting zone is operated with a water tohydrocarbon volumetric ratio from about 1:100 to about 20:100.
 5. Theprocess of claim 1 wherein said caustic/hydrocarbon contacting zone isoperated with an aqueous caustic solution to hydrocarbon volumetricratio from about 1:100 to about 20:100.
 6. The process of claim 1wherein said aqueous caustic scrubbing solution contains sodiumhydroxide.